1. Field of the Invention
The present invention relates to a lithium ion battery. Specifically, the invention relates to a lithium ion battery including a negative electrode on which a film derived from an oxalato complex compound is formed.
2. Description of Related Art
In a nonaqueous secondary battery such as a lithium ion battery, a nonaqueous electrolytic solution may contain a film forming agent (for example, a compound containing an oxalato complex as an anion), for example, in order to improve durability (refer to Japanese Patent Application Publication No. 2013-182712 (JP 2013-182712 A) and Japanese Patent Application Publication No. 2013-247009 (JP 2013-247009 A)). In such a battery, typically, the film forming agent is reduced and decomposed during initial charging. A stable film is formed on a surface of a negative electrode. As a result, further decomposition of the nonaqueous electrolytic solution and deterioration of an active material can be suppressed, and the durability of the battery can be improved.
However, for example, in a large-sized battery having a large electrode body (wide electrode area), the penetration amount of a film forming agent varies in a penetration direction of a nonaqueous electrolytic solution (typically, at an end portion and the center of the electrode body in a width direction thereof), and thus the thickness of a film formed in the penetration direction may be non-uniform. As a technique relating to this problem, for example, JP 2013-182712 A discloses a lithium ion battery in which at least one member of a positive electrode, a negative electrode, and a separator includes a surface-modified portion (a portion in which the impregnating ability of a nonaqueous electrolytic solution is improved) that is provided at the center of the member in a width direction thereof.